Method and systems for laser treatment of presbyopia using offset imaging

ABSTRACT

An ophthalmic surgery system and method for treating presbyopia by performing ablative photodecomposition of the corneal surface. The offset image of a variable aperture, such as a variable width slit and variable diameter iris diaphragm, is scanned in a preselected pattern to perform ablative sculpting of predetermined portions of a corneal surface. The scanning is performed to ablate an optical zone sized to match the patient pupil with a peripheral transition zone outside the pupil. The shape of the ablated optical zone is different from the shape of the final optical correction on the anterior surface of the cornea. The optical zone corrects for near-vision centrally and far-vision peripherally. A movable image displacement mechanism enables radial displacement and angular rotation of the profiled beam exiting from the variable aperture. The invention enables wide area treatment with a laser having a narrower beam than the treatment area, and can be used in the treatment of many conditions in conjunction with presbyopia such as hyperopia, hyperopic astigmatism and irregular refractive aberrations.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application is a continuation application, which claimspriority from co-pending U.S. Divisional patent application Ser. No.09/901,964 filed on Jul. 9, 2001, which claims priority from U.S. patentapplication Ser. No. 09/261,768, filed Mar. 3, 1999 (now U.S. Pat. No.6,280,435), which claims priority under 37 CFR §1.78(a) from ProvisionalApplication No. 60/076,786, filed on Mar. 4, 1998, the full disclosuresof which are hereby incorporated herein by reference.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

[0002] NOT APPLICABLE

REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK

[0003] NOT APPLICABLE

BACKGROUND OF THE INVENTION

[0004] 1. Field of the Invention

[0005] This invention relates to surgical modifications to the eye. In aspecific embodiment, the invention provides ophthalmic surgerytechniques which employ a laser to effect ablative photodecomposition ofcorneal tissue to correct presbyopia and/or other vision defects.

[0006] With aging, a condition of the eye known as presbyopia develops.With this condition, the crystalline lens of the eye loses the abilityto focus on near objects when the eye is corrected for far-vision.

[0007] Presbyopia is often treated with bifocal eyeglasses. Withbifocals, one portion of the lens is corrected for far-vision, andanother portion of the lens is corrected for near-vision. By lookingdown through the bifocals, the user looks through the portion of thelens corrected for near-vision. When viewing distant objects, the userlooks higher, through the portion of the bifocals corrected forfar-vision.

[0008] Efforts have been made to treat presbyopia using partitionedlenses positioned directly over the pupil of the eye. Examples includemultifocal contact lenses. Unfortunately, when presbyopia is correctedwith bifocal or multifocal lenses attached to the cornea, the user issimultaneously looking through the near- and far-vision correctedlenses. As a result, the user will see both in-focus and out-of-focusimages simultaneously when viewing an object. This out-of-focus imagesuperimposed on the in-focus image can cause glare and degrade visionwhen viewing objects at low contrast.

[0009] Another technique for treating presbyopia has been to correct oneeye of the patient for near-vision and to correct the other eye fordistance-vision. This technique is known as monovision. With monovision,a patient uses one eye to see distant objects and the other eye to seeclose objects. Unfortunately with monovision, the patient may notclearly see objects that are intermediately positioned because theobject is out-of-focus for both eyes. Also, a patient may have troubleseeing with only one eye.

[0010] Laser-based systems and methods are known for enabling ophthalmicsurgery on the cornea in order to correct vision defects by thetechnique known as ablative photodecomposition. Changing the shape ofthe anterior surface of the cornea will change the optical properties ofan eye. These ablative photodecomposition systems and methods controlultraviolet laser radiation flux density and exposure time upon thecornea so as to achieve a desired surface change in the cornea andthereby correct an optical defect.

[0011] Several different ablative photodecomposition techniques havebeen described to correct specific optical errors of the eye. Forexample, a myopic condition may be corrected by laser sculpting acorneal surface to reduce curvature. An astigmatic condition, which istypically characterized by a cylindrical component of curvature(departing from the otherwise generally spherical curvature of thecornea), can be corrected by a cylindrical ablation. Laser sculpting acorneal surface to increase the curvature can correct a hyperopiccondition.

[0012] In a typical laser surgical procedure, the optically functionalregion of the corneal surface to be ablated is designated the opticalzone. Depending on the nature of the desired optical correction, theoptical zone may or may not be centered on the center of the pupil or onthe apex of the anterior corneal surface. One technique for increasingthe curvature of the optical zone for hyperopia error correctioninvolves selectively varying the area of the cornea exposed to the laserbeam radiation so as to produce an essentially spherical surface profileof increased curvature. This selective variation of the irradiated areamay be accomplished in a variety of ways. For example, the optical zonecan be scanned with a laser beam having a relatively smallcross-sectional area (compared to the optical zone) in such a mannerthat the ablation depth increases with distance from the intended centerof ablation. The result is a substantially spherical profile for theanterior corneal surface with maximum depth of cut at the extreme outerboundary of the optical zone. Another technique for sculpting theoptical zone employs a rotatable mask having a plurality of apertures.The apertures are sequentially introduced into the laser beam path toprovide progressive shaping of the laser beam in order to achieve thedesired profile.

[0013] Efforts have also been made to treat presbyopia using ablativephotodecomposition. One specific technique of treating presbyopiacreates near-vision correction by ablating a region of the lower portionof the cornea adjacent the pupil rim. With this eccentric positioning ofthe ablation, the near-vision lens is not centered over the pupil.Consequently, constriction of the pupil may occlude the ablatednear-vision lens. Constriction of the pupil is a natural response of theeye to illumination, and could potentially disrupt near-vision.

[0014] Alternative suggested presbyopia treatments include laserablation of a small annular region of the cornea (having a diameter notexceeding 3.5 mm), or the ablation of a central lens for near-vision,surrounded by a gradual blend zone, and then a peripheral farvisionlens, all within the optically used portion of the cornea.

[0015] Efforts have been made in the past to laser sculpt a transitionzone to provide a more gradual sloping of the walls and to eliminate thesharp discontinuity between the ablation zone and the surroundinguntreated cornea. These efforts have included the use of a beam rotationor scanning mechanism operated by a computer to provide programmedablation of the transition zone to achieve a sigrnoid or other profile.While somewhat effective, these efforts often suffer from the addedcomplexity of additional optical elements, such as a rotatable off-axismirror or revolving prism having suitable optical properties.

[0016] 2. Description of the Background Art

[0017] Systems and methods relevant to laser-based treatments forpresbyopia are disclosed in the following U.S. patents and patentapplications, the entire disclosures of which are hereby incorporated byreference: U.S. Pat. No. 5,395,356, issued Mar. 7, 1995, entitled“Correction of Presbyopia by Photorefractive Keratectomy”; U.S. Pat. No.5,533,997, issued Jul. 9, 1996, entitled “Apparatus and Method forPerforming Presbyopia Correction”; and U.S. Pat. No. 5,314,422, issuedMay 24, 1994, entitled “Equipment for the Correction of Presbyopia byRemodeling the Corneal Surface by Means of Photoablation.”

[0018] Ablative photodecomposition systems and methods are disclosed inthe following U.S. patents and patent applications, the entiredisclosures of which are hereby incorporated by reference: U.S. Pat. No.4,665,913, issued May 19, 1987, entitled “Method for OphthalmicalSurgery”; U.S. Pat. No. 4,669,466, issued Jun. 2, 1987, for “Method andApparatus for Analysis and Correction of Abnormal Refractive Errors ofthe Eye”; U.S. Pat. No. 4,732,148, issued Mar. 22, 1988, entitled“Method for Performing Ophthalmic Laser Surgery”; U.S. Pat. No.4,770,172, issued Sep. 13, 1988, entitled “Method of Laser Sculpture ofthe Optically Used Portion of the Cornea”; U.S. Pat. No. 4,773,414,issued Sep. 27, 1988, entitled “Method of Laser Sculpture of theOptically Used Portion of the Cornea”; U.S. patent application Ser. No.07/109,812, filed Oct. 16, 1987, entitled “Laser Surgery Method andApparatus”; U.S. Pat. No. 5,163,934, issued Nov. 17, 1992, entitled“Photorefractive Keratectomy”; U.S. Pat. No. 5,556,395, issued Sep. 17,1996, entitled “Method and System for Laser Treatment of RefractiveError Using an Offset Image of a Rotatable Mask”; U.S. patentapplication Ser. No. 08/368,799, filed Jan. 4, 1995, entitled “Methodand Apparatus for Temporal and Spatial Beam Integration”; U.S. patentapplication Ser. No. 08/058,599, filed May 7, 1993, entitled “Method andSystem for Laser Treatment of Refractive Errors Using Offset Imaging”;U.S. Pat. No. 5,683,379, issued Nov. 4, 1997, entitled “Apparatus forModifying the Surface of the Eye Through Large Beam Laser Polishing andMethod of Controlling the Apparatus”; and U.S. Pat. No. 5,827,264,issued Oct. 27, 1998 entitled “Method of Controlling Apparatus forModifying the Surface of the Eye Through Large Beam Laser Polishing.”

[0019] Techniques for treating presbyopia with contact lenses aredisclosed in the following U.S. patents and patent applications, theentire disclosures of which are hereby incorporated by reference: U.S.Pat. No. 5,835,192, issued Nov. 10, 1998, entitled “Contact Lens andMethod of Fitting a Contact Lens”; U.S. Pat. No. 5,485,228 issued Jan.16, 1996 entitled “Multifocal Ophthalmic Lens Pair;” and U.S. Pat. No.5,864,379 issued Jan. 26, 1999 entitled “Contact Lens and Process forFitting.”

BRIEF SUMMARY OF THE INVENTION

[0020] It is an object of the invention to mitigate and/or inhibitpresbyopia with minimal vision degradation by ablating a transition zoneperipheral to an optical zone. It is a further object of the inventionto ablate a cornea to produce a healed cornea with an aspheric opticalzone that corrects presbyopia. In one aspect, the invention provides forablating the cornea to a desired shape that compensates for changes inthe corneal shape as the cornea heals. In another aspect, the inventionprovides for the simultaneous correction of presbyopic and otherrefractive corrections such as nearsightedness, farsightedness andastigmatism. In a yet further aspect, the invention provides for scalingthe aspheric optical zone to match the size of the pupil. In yet anotheraspect, the invention provides for a method for treating presbyopiawhich includes ablating a transition zone outside an optical zone.

[0021] One of the major difficulties encountered in the application oflaser surgery techniques to effect hyperopic and presbyopic refractiveerror corrections lies in the nature of the boundary between the opticalzone and the untreated area. When the anterior surface of the cornea issculpted to have an increased curvature, the maximum depth of cut occursat the outer boundary of the optical zone. The generally annular regionbetween this outer boundary and the adjacent untreated anterior surfaceportion of the cornea typically exhibits steep walls after thecompletion of the photoablation procedure. After the surgery, the eyetends to eliminate these steep walls with a stimulated healing responseinvolving concurrent epithelial cell growth and stromal remodeling bythe deposition of collagen, which results in corneal smoothing byfilling in tissue in the steep walled region. This natural healingresponse acts to eliminate the discontinuity, resulting in a buildup oftissue in the steep walled region and over the outer portion of theoptical zone. This natural phenomenon, sometimes termed the “hyperopicshift” in phototherapeutic keratectomy, causes a lack of precision for agiven surgical procedure and diminished predictability, counteractingthe beneficial effects of the refractive correction procedure andthereby reducing the desirability of the procedure to the prospectivepatient.

[0022] According to the present invention, the ablated surface can becontoured to provide an aspheric surface on a healed cornea. Theinvention provides for adjusting the ablation to compensate for factorseffecting the final geometry of the healed cornea. These factors includecorneal healing and the spatial variation of ablation. The shape oftissue ablated with a uniform laser beam pulse will depend upon the sizeand shape of the laser beam spot. The spatial variation of the totalablation may also cause variations in the ablated corneal shape. Forexample, a hyperopic ablation intended to produce a spherical ablationmay demonstrate greater steepening near the center of the optical zone.This increased central curvature may form an aspheric surface thatcorrects for presbyopia.

[0023] The ablated surface is covered following the surgery, typicallyby a new epithelial layer or a repositioned anterior flap of the cornealtissue. Consequently, the final shape of the anterior surface of thecornea may be a different shape than the ablated shape. However, it isthe final change in shape of the anterior surface of the cornea, not theinitial ablated surface, which determines the refractive change effectedby the surgery. Therefore, it may be desirable to ablate a shape on thecornea that is different from the final intended shape on the anteriorsurface of the cornea. For example, the optical zone may be ablated to asubstantially spherical shape for correcting hyperopia. This ablatedsurface may then heal to an aspheric surface that corrects presbyopia.

[0024] The invention includes a method and system for performingablative photodecomposition of the corneal surface that is capable ofproviding relatively smooth transition zones along with accuratesculpting of the anterior or other corneal surface to effectsimultaneous symmetric or asymmetric refractive and presbyopiccorrections with relatively large area coverage. The inventionpreferably employs a laser beam of smaller beam size than the totaltreatment area.

[0025] The invention further provides for the ablation of an opticalzone that substantially matches the area of the pupil. For presbyopicpatients, the maximum pupil diameter is typically about 5 mm. Therefore,it is an aspect of the invention that the ablated optical zone have adiameter of about 5 mm, and be user selectable (by the user of theablation system) to a diameter between 3 and 7 mm. The optical zone ispreferably ablated to form a healed aspheric surface. Preferably, thecentral portion of the optical zone provides near-vision correction andthe peripheral portion of the optical zone provides far-visioncorrection.

[0026] The invention additionally provides for scaling a diameter of theaspheric surface to the pupil. This scaling of the aspheric surfacepermits an appropriate balance between near and far-vision correctionwithin the pupil. For example, a patient with a 5 mm diameter pupil mayhave a 2.5 mm diameter zone corrected for near-vision, while a patientwith a 3 mm diameter pupil may have a 1.5 mm diameter zone corrected fornear-vision. Scaling of the aspheric lens may be based on areas of thepupil and/or aspheric surface.

[0027] The invention also provides for ablating a transition zoneperipheral to the optical zone and to the pupil. This positioning of theablated transition zone will produce optimal results once the corneaheals. The ablated transition zone provides greater control over thehealing process and provides greater control of the shape of the healedsurface within the adjacent optical zone. Because the transition zone isablated to control the shape of an adjacent healed surface, thetransition zone may produce a corneal shape which corrects for neithernear- nor far-vision. Thus, the transition zone is preferably positionedoutside the pupil. Further, the transition zone is preferably sized sothat healing of the cornea can be controlled within the adjacent opticalzone. The optimal size of the transition zone is an annular regionextending radially outward about 2 mm from the outer edge of the ablatedoptical zone. An ablation with a 5 mm diameter ablated optical zone andan optimally sized ablated transition zone will extend about 9 mm acrossthe cornea. Transition zones of other sizes may be ablated outside theoptical zone. Dimensions of the transition zone extending radiallyoutward from the optical zone range from about 1 to 3 mm and preferablyfrom about 1.5 to 2.5 mm.

[0028] In a first aspect, the present invention provides a method forreprofiling an anterior surface of the cornea of the eye. The anteriorsurface is reprofiled from an initial shape to a multifocal asphericshape for correcting presbyopia. The method comprises aligning a lasersystem with the eye. The laser system is operable to deliver ablativeradiation to the cornea. A surface of the cornea is ablated to a desiredshape by selectively exposing the cornea to the ablative radiation. Thecornea is ablated to an ablated shape so that an optical zone extendsacross the pupil and so that a transition zone is disposed beyond thepupil. The ablated surface is covered to produce a final asphericanterior corneal surface.

[0029] In some embodiments, the covering step will comprise regeneratingan epithelial layer over an ablated anterior surface of the cornea. Inother embodiments, the covering step will comprise repositioning a flapof the cornea over the eye after a portion of either the flap, or theunderlying corneal tissues, has been ablated.

[0030] In another aspect, the present invention provides an ophthalmicsurgery system for performing selective ablation of a corneal surface ofthe eye so as to create a desired aspheric shape for correctingpresbyopia on the anterior surface of a healed cornea. The systemcomprises means for directing a laser beam along a path. Means are alsoprovided for profiling the beam to produce a profiled beam with acenter. Means for displacing the center of the profiled beam over anarea of the corneal surface will generally be coupled to the profilingmeans. A computer controls the positioning of the beam center over thearea, and creates a plurality of successive laser beam pulses. Theposition of the plurality of pulses is determined by a laser treatmenttable that is scaled to a dimension of a pupil.

[0031] In another aspect, the present invention provides a laser eyesurgery method comprising selectively ablating corneal tissue from aneye having an uncorrected surface shape. Corneal tissue is ablated so asto produce an initial ablated shape on an anterior surface of the corneaof the eye. The ablated eye heals, and the healed eye has a healedanterior surface shape which differs significantly from the initialablated shape. This healed shape substantially, and in some instancesentirely, corrects a refractive error of the eye.

[0032] In yet another aspect, the present invention provides a laser eyesurgery method comprising selectively ablating corneal tissue from aneye having a refractive error. The refractive error is selected from thegroup consisting of myopia, hyperopia, and astigmatism. The ablatingstep removes a portion of cornea so as to simultaneously correct therefractive error and mitigate presbyopia of the eye.

[0033] In yet another aspect, the present invention provides a methodfor treating presbyopia of an eye. The eye has a pupil, and the methodcomprises selectively ablating corneal tissue from the eye so as toproduce an ablated corneal surface. The corneal surface has an opticalzone, and a transition zone surrounding the optical zone. The opticalzone of the corneal surface defines an aspheric shape to mitigate thepresbyopia, and a dimension of the optical zone substantially matches adimension of the pupil under scotopic conditions.

[0034] In yet another aspect, the present invention provides a methodfor treating presbyopia of an eye. The eye has a pupil, and the methodcomprises selectively ablating corneal tissue from the eye so as toproduce a corneal surface having an optical zone, and a transition zonesurrounding the optical zone. The optical zone of the corneal surfacedefines an aspheric shape to mitigate the presbyopia. The transitionzone is disposed outside of the pupil.

[0035] For a fuller understanding of the nature and advantages of theinvention, reference should be had to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036]FIG. 1 is a side sectional view of an eye treated for presbyopiawith the invention.

[0037]FIG. 2 is a side sectional view of an ablation profileillustrating the effect of corneal healing on ablation shape.

[0038]FIG. 3 illustrates the refractive power over the pupil of anaspheric surface for treating presbyopia.

[0039]FIG. 4 is a block diagram of an ophthalmic surgery system forincorporating the invention.

[0040]FIG. 5 is a schematic plan view illustrating a movable slit andvariable diameter aperture used in the system 20 of FIG. 4.

[0041]FIG. 6 is a schematic diagram illustrating the offset lensprinciple.

[0042]FIG. 7 is a schematic diagram illustrating the lens offset viewedalong the axis of rotation.

[0043]FIG. 8 is a schematic view showing the ablation geometry for theaperture of FIG. 5.

[0044]FIG. 9 is a schematic view of the delivery system optics.

[0045]FIG. 10 illustrates an ablation profile on a corneal surface incomparison to an intended +3 D spherical optical correction.

[0046]FIG. 11 illustrates an optical correction on a healed anteriorcorneal surface in comparison to an intended +3 D spherical opticalcorrection.

[0047]FIG. 12 illustrates the effect of covering and healing over anablated optical zone.

[0048]FIG. 13 illustrates an initial ablated shape derived from adesired shape and a healing-induced change.

[0049]FIG. 14 illustrates overcorrecting and restricting an ablatedsurface shape relative to a desired anterior surface correction.

[0050]FIG. 15 illustrates a small untreated zone centered on the opticalzone of an ablated surface.

DETAILED DESCRIPTION OF THE INVENTION

[0051] Turning now to the drawings, FIG. 1 illustrates a schematic sideview of a cornea 200 treated with the invention. The cornea 200 has ananterior surface that provides most of the refractive power of the eye.The initial anterior surface 205 of the cornea 200 has been reshaped toa desired healed profile. The desired healed profile includes anterioroptical surface 210 and anterior transition surface 215. The anterioroptical surface 210 has a multifocal aspheric shape that corrects fornear-vision centrally and far-vision peripherally.

[0052] While the present invention will often be described withreference to the mitigation of presbyopia in combination with refractivehyperopia treatment, it should be understood that the benefits of thepresent invention are not limited to these specific procedures. Thesepresbyopia treatment techniques may be used when no other refractivecorrection (other than the correction, mitigation, and/or inhibition ofpresbyopia) is desired, or the present treatment may be combined withtherapies for one or more of myopia, astigmatism, irregular refractiveaberrations, and the like, as well as with hyperopia. Still otheraspects of the present invention, including methods and systems whichaccommodate and adjust for reepithelization, may find uses in a broadvariety of ophthalmic procedures.

[0053] The peripheral positioning of the far-vision correctionadvantageously permit distance viewing when the pupil is dilated atnight. Anterior transition surface 215 is the anterior surface of thecornea that provides a gradual change in shape between anterior opticalsurface 210 and the portion of the cornea retaining the initial anteriorsurface 205. The outer boundary 212 of the anterior optical surfacepreferably extends entirely across, and is ideally substantiallycoextensive with, the pupil which is bounded by iris 220. The light rayspassing through anterior transition surface 215 do not contribute to theimage formed by anterior optical surface 210. Therefore, anteriortransition surface 215 is desirably positioned outside the pupil. Thispositioning of anterior transition surface 215 causes the light rayspassing through anterior transition surface 215 to be substantiallyoccluded by iris 220. This occlusion improves patient vision because thelight rays are blocked that do not contribute to image formation, andwhich would otherwise reduce the contrast of the image.

[0054] The optical correction effected by an ablative surgical procedureto the cornea is derived from a change in the anterior corneal surfacefrom an initial anterior surface 205 to post-operative anterior opticalsurface 210. The anterior optical correction is the post-operativeanterior optical surface 210 minus the initial anterior surface 205. Anablation profile is a change in an exposed surface profile occurringimmediately after the tissue removal process. Therefore, the ablationprofile is the exposed surface profile immediately after the tissueremoval process minus the initial exposed surface profile. As usedherein, “ablated shape” can refer either to an ablation-induced changein a surface topography on a surface of the cornea, or to the surfacetopography of the cornea after ablation. Similarly, “healed shape” canmean either a final comeal topography once healing is complete, or achange in the corneal topography from an initial topography to a finalcorneal topography once healing is complete. A healed shape differssignificantly from an ablated shape when a difference between the twoshapes is sufficient to be perceptible by a patient. Healing can refereither to an initial covering of an ablated surface contour or changesin a tissue structure of the cornea following an initial covering of anablated surface contour.

[0055] The relationship of the ablated surface and the anterior cornealsurface overlying the ablated surface is shown in FIG. 2. Initialablated surface 202 includes ablated optical zone 211 and ablatedtransition zone 216. Ablated optical zone 211 includes ablated centraloptical zone 231 for the correction of near-vision, ablated peripheraloptical zone 241 for the correction of far-vision, and ablatedintermediate optical zone 236 for the correction of vision intermediateto near- and far-vision. Ablated central optical zone 231 is shaped toappropriately form anterior central optical surface 230 when ablatedsurface 202 is covered and cornea 200 is healed to form anterior opticalsurface 210. Ablated intermediate optical zone 236 is shaped to formanterior intermediate optical surface 235 when ablated surface 202 iscovered and cornea 200 is healed. Ablated peripheral optical zone 241 isshaped to appropriately form anterior peripheral optical surface 240when ablated surface 202 is covered and cornea 200 is healed. Ablatedtransition zone 216 is ablated to minimize the effect of corneal healingon anterior optical surface 210.

[0056] In one embodiment, covering of the ablated shape will cause thefinal shape of anterior optical surface 210 of the anterior surface ofcornea 200 to be different from ablated optical zone 211. This aspect ofthe present invention is more fully described in the publicationentitled “Corneal Ablation Profilometry and Steep Central Islands,”Journal of Refractive Surgery, 1997, Vol. 13, pp. 235-45, the entiredisclosure of which is herein incorporated by reference.

[0057] Initial ablated shape 202 is covered after the ablation.Proximity to ablated transition zone 216 may cause anterior peripheraloptical surface 240 to be a different shape than underlying ablatedperipheral optical zone 241. However, anterior central optical surface230 of anterior optical surface 210 is distant from ablated transitionzone 216. Therefore the shape of anterior central optical surface 230will more closely match the shape of ablated central optical zone 231.In one aspect, the covering may include regeneration of the epitheliallayer following ablation of Bowman's membrane and adjacent stromallayers. In another aspect, covering includes replacing a resectedportion of the cornea as is described in U.S. Pat. No. 4,903,695, issuedFeb. 27, 1990, entitled “Method and Apparatus for Performing aKeratomileusis or the Like Operation.” In this aspect, the resectedportion includes an epithelial layer. In a yet further aspect ofcovering, a tear film forms over the epithelial layer to form theanterior surface when cornea 200 is fully healed. The final shape ofanterior optical surface 210 will substantially determine the opticalproperties of the cornea. Therefore, it may be desirable to ablatecornea 200 to form ablated optical zone 211 that is a different shapethan the shape of anterior optical surface 210.

[0058] In another embodiment, ablated optical zone 211 includes ablatedcentral optical zone 231 and ablated peripheral optical zone 241.Ablated intermediate optical zone 241 may be replaced by extendingablated peripheral optical zone 241 and ablated central optical zone 231to border one another. Ablated central optical zone 231 provides about2.5 D of near-vision correction with a range from about 0.5 to 4 D,preferably about 2 to 3 D and a diameter from about 1.0 to 3.5 mm andpreferably from about 2 to 3 mm. Ablated peripheral optical zone 241 isablated to provide far-vision correction and is sized to extend radiallyoutward from the outer boundary of ablated central optical zone 231 to adiameter of about 5 mm with a range from about 3 to 7 mm and preferablyfrom about 4 to 6 mm. Ablated transition zone 216 extends radiallyoutward from the outer boundary of ablated optical zone 211 to adiameter of about 9 mm with a range from about 6 to 11 mm and preferablyfrom about 7 to 10 mm. Covering of ablated optical zone 211 will causeanterior intermediate optical surface 240 to form over the borderbetween ablated central optical zone 231 and ablated peripheral opticalzone 241. Anterior central optical surface 230 will form over ablatedcentral optical zone 231. Anterior peripheral optical surface 240 willform over ablated peripheral optical zone 241. Therefore, anterioroptical surface 210 may be formed as a multifocal aspheric surface oncornea 200 by ablating only two optical zones within ablated opticalzone 211.

[0059] An illustrative plot of the relative refractive power of anterioroptical surface 210 as a function of radial position across the pupil isshown in FIG. 3. The refractive power decreases from the center towardthe periphery. Anterior central optical surface 230 of cornea 200 has arelative refractive power from about 1 to 4 D, and preferably from about2 and 3 D that corrects for near-vision. This central surface rangesfrom about 1 to 3 mm in diameter and preferably from about 1.5 to 2.5 mmin diameter. Anterior peripheral optical surface 240 corrects forfar-vision. This peripheral surface has an inner boundary from about 2and 4 mm in diameter and an outer boundary 212 that may be scaled tomatch the outer boundary of the pupil as shown in FIG. 1. Outer boundary212 may be scaled to a diameter of between about 3 and 7 mm. Anteriorintermediate optical surface 235 has continuously varying refractivepower. This region is desirable and provides focus for objectsappropriately positioned intermediate to near and far positions.

[0060] In an exemplary embodiment, ablated central optical zone 231,ablated intermediate optical zone, 236 and ablated peripheral opticalzone 241 are scaled to match a dimension of the pupil. The scalingdimensions may be an area of the pupil, a diameter of the pupil, aradius, or the like. For example, ablated optical zone 211 may bedecreased by about 20% from a diameter of about 5 mm to 4 mm for apatient with a 4 mm diameter pupil. In this case, ablated centraloptical zone 231, ablated intermediate optical zone 236 and ablatedperipheral optical zone 241 are each decreased by about 20%. Thisscaling is desirable because it keeps the ratios of near, intermediateand far-vision nearly constant for varying pupil size. The innerboundary of ablated transition zone 216 is scaled to border the outerboundary of ablated optical zone 211. During the scaling of ablatedoptical zone 211, the outer boundary of ablated transition zone 216 maybe scaled to match the scaling of ablated optical zone 211.Alternatively, the outer boundary of ablated transition zone 216 may befixed to a constant value while the inner boundary of ablated transitionzone 216 is varied.

[0061]FIG. 4 illustrates a block diagram of an ophthalmic surgery systemfor incorporating the invention. As seen in this Figure, a personalcomputer (PC) work station 10 is coupled to an embedded computer 21 of alaser surgery unit 20 by means of a first bus connection 11. The PC workstation 10 comprises a tangible medium 12 and a treatment table 14. Thelaser treatment table 14 includes a listing of coordinate references ofthe laser beam during an ablation of the cornea. The sub-components oflaser surgery unit 20 are known components and preferably comprise theelements of the VISX STAR™ EXCIMER LASER SYSTEM and of the STAR S2™System available from VISX, INCORPORATED of Santa Clara, Calif. Thus,the laser surgery system 20 includes a plurality of sensors generallydesignated with reference numeral 22 which produce feedback signals fromthe movable mechanical and optical components in the laser opticalsystem, such as the elements driven by an iris motor 23, an imagerotator 24, an astigmatism motor 25 and an astigmatism angle motor 26.The feedback signals from sensors 22 are provided via appropriate signalconductors to the embedded computer 21. The embedded computer 21controls the operation of the motor drivers generally designated withreference numeral 27 for operating the elements 23-26. In addition,embedded computer 21 controls the operation of the excimer laser 28,which is preferably an argon-fluorine laser with a 193 nanometerwavelength output designed to provide feedback stabilized fluence of 160mJoules per square centimeter at the cornea of the patient's eye 30 viathe delivery system optics generally designated with reference numeral29 and shown in FIG. 9. Other lasers having a suitable wavelength may beused to make an ablative energy for removing a tissue from the eye. Forexample, solid state lasers such as a yittrium aluminum garnet (YAG)laser producing a fifth harmonic of a fundamental wavelength may be usedto generate an ablative energy. Other ancillary components of the lasersurgery system 20 which are not necessary to an understanding of theinvention, such as a high resolution microscope, a video monitor for themicroscope, a patient eye retention system, and an ablation effluentevacuator/filter, as well as the gas delivery system, have been omittedto avoid prolixity. Similarly, the keyboard, display, and conventionalPC subsystem components (e.g., flexible and hard disk drives, memoryboards and the like) have been omitted from the depiction of the PC workstation 10. If desired, embedded computer 21 may be constructed with PCwork station components and built into laser surgery system 20. In thiscase embedded computer 21 may supplant PC workstation 10.

[0062] The iris motor 23 is used to control the diameter of a variablediameter iris schematically depicted in FIG. 5. The astigmatism motor 25is used to control the separation distance between a pair of cylinderblades 35, 36 which are mounted on a platform 38 for bi-directionaltranslational motion in the direction of arrows 40, 41. Platform 38 isrotatably mounted on a second platform (not illustrated) and isrotationally driven by astigmatism angle motor 26 in a conventional wayin order to enable alignment of the slit axis (illustrated in a verticalorientation in FIG. 5) with the appropriate coordinate axes of thepatient's eye. Iris 32 is driven by iris motor 23 in a known way tochange the diameter of the iris opening from a fully opened position(the position illustrated in FIG. 5) to a fully closed position in whichthe aperture is closed to a minimum diameter of 0.8 mm. It is understoodthat the variable diameter iris 32 and the cylinder blades 35, 36 arepositioned with respect to the output of laser 28 in such a manner as tointercept the beam prior to irradiation of the corneal surface of thepatient's eye 30. For the purpose of this application, it may be assumedthat iris 32 and cylinder blades 35, 36 are part of the delivery systemoptics subunit 29 shown in FIG. 4.

[0063] The system of FIGS. 4 and 5 is used according to the invention toeffect presbyopic, hyperopic, myopic, astigmatic, and other errorcorrections to the anterior surface of the cornea, to provide a smoothtransition zone between the outer edge of the optical zone and theuntreated surface of the cornea, and to effect surface smoothing whendesired. Other techniques besides the above area profiling of a laserbeam may be used to profile the laser beam to a desired size and energydistribution on the surface of the eye. For example a lens may be usedto profile a beam exiting from an aperture by focusing the beam to asuitably small area and desired energy profile as described in U.S. Pat.No. 4,718,418, the full disclosure of which is herein incorporated byreference. Also a diffractive optic may be used to adjust an energyprofile of the laser beam on the surface of the eye as described incopending application entitled Laser Delivery System and Method withDiffractive Optic Beam Integration, U.S. patent application Ser. No.09/015,841 filed on Jan. 29, 1998 the full disclosure of which is hereinincorporated by reference.

[0064] With reference to FIG. 6, an imaging lens 51 is laterally offsetfrom an axis 52 by a variable amount in the manner set forth more fullybelow. Lens 51 preferably comprises the existing imaging lens found inthe delivery system optics 29 of the FIG. 4 system. Axis 52 is the axiscorresponding to the center of rotation of lens 51. Displacing lens 51by translating the lens in a radial direction off the axis 52, which mayor may not correspond to the laser beam axis, displaces the image 54 ofaperture 53 in a related manner. By also rotating lens 51 about the axis52 in an eccentric fashion, as illustrated in FIG. 7, the displacedimage 54 of aperture 53 can be scanned about axis 52. This scanning isalong a preselected path, which in the hyperopic correction proceduredescribed below is an annular path about the axis 52. Depending upon themanner in which the lens offset, lens rotation, slit width, slitrotation and iris diameter are controlled, various types of ablationcorrections can be effected. These corrections include presbyopiacorrection, hyperopic error corrections, hyperopic astigmatismcorrections, and other vision error corrections, along with simultaneousor successive edge contouring to form a smooth transition zone.

[0065]FIG. 8 illustrates the aperture positioning relative to theintended ablation center when employing the variable diameter iris 32and cylinder blades 35, 36 of FIG. 5 to effect a refractive errorcorrection. In this Figure, R2 represents the half width of the slitbetween blades 35, 36, Ri is the radius of the iris 32, r is the radiusof a circle covered by the aperture, s is the radial offset of thecenter of the image of the slit aperture relative to the center ofrotation 52, and 0 is the half angle for which the circle of radius r iscovered by the aperture. The intended ablated optical zone is thecentral region bounded by circle 61 and the intended ablated transitionzone is the annular region bounded by circles 61 and 62.

[0066] The manner in which the slit width and diameter are varied by thecomputer depends upon the type of vision correction desired. For ahyperopic correction, a fixed value of the refractive correction may beused to generate the cut profile C(r). For a hyperopic refractivecorrection of a given fixed value, the sequencing of the aperture isdone in such a manner as to satisfy the hyperopic lens equationsdescribed in “Photorefractive Keratectomy: A Technique for LaserRefractive Surgery” authored by Munnerlyn et al., J. Cataract Refract.Surg. Vol. 18, pages 46-52 (Jan., 1988), the entire disclosure of whichis hereby incorporated by reference. Also, European Patent Officepublication number EP 0 628 298 A1, published Dec. 14, 1994, disclosesan aperture sequencing for correcting hyperopia, the entire disclosureof which is hereby incorporated by reference.

[0067] For the correction of presbyopia, it may be desirable to vary therefractive power across the ablated surface. The cut profile C(r) may becalculated by calculating the incremental cut profiles along thesurface. The incremental cut profiles are then summed to calculate theoverall cut profile C(r). The incremental cut profiles may be calculatedusing the above hyperopic lens equation, the desired ablated refractivecorrection, and the position from the center of the aspheric lens.

[0068] The cut profile is given by the equation:

C(r)=(d/π)Σi(n _(i)θ(r))   (1)

[0069] where n_(i) is the number of laser pulses for the i^(th) aperturein a sequence of aperture dimensions and radial positions, and d is theamount of material removed with each laser pulse or a scaling factorwhich also takes into account corneal healing. Once the cut profile hasbeen calculated, the sequence of aperture dimensions and pulses may becalculated. The sequence of aperture dimensions is created by control ofthe width of the slit and the diameter of iris 32 throughout thesurgical procedure. The sequence of aperture dimensions and positionsare preferably incorporated into a laser treatment table.

[0070] The sequence of aperture dimensions may also be tailored toaccommodate variations in the ablation profiles of individual pulsesfrom the laser beam. For example, the spatial variation of tissueablation may cause the geometry of tissue ablated with a single laserpulse to be deeper at the edges of an ablation adjacent the image ofiris 32 and cylinder blades 35 and 36. For an individual laser pulse,this increased ablation depth near the edge of an ablation may be 50%greater than the central ablation depth. Therefore, a 4D intendedhyperopic ablation that assumes a uniform layer of tissue is removedwith each laser pulse will ablate about 6 D of correction near thecenter of ablated optical zone 211. Clinically, the inventors haveobserved that patients treated with the above ablation algorithm for 3to 4 D of hyperopia have also been successfully treated for presbyopia.However, with a +2D correction, the correction of presbyopia is onlypartial. Therefore to correct presbyopia and hyperopia, it may bedesirable to combine the +2 D correction with an aspheric ablation. Inthis case, the aspheric correction is about one half of the asphericcorrection that would be ablated on an eye with no refractive error.

[0071] Preferably, the refractive correction of cut profile C(r) isscaled to match a dimension of the pupil. This scaling may be achievedby appropriately varying the refractive correction entered into thehyperopic lens equation. For example, consider the scaling of anablation for a 5 mm pupil compared to a 4 mm pupil. If the asphericsurface includes a 1.5D ablated curvature 1.25 mm from the aspheric lenscenter for the 5 mm pupil, this 1.5D curvature will be ablated 1.0 mmfrom the aspheric lens center on a 4 mm pupil. This scaling maintains abalance of near and far-vision correction by accommodating individualvariability in pupil size. By scaling the cut profile C(r), the scalingof the ablated optical zone is incorporated into the laser treatmenttable.

[0072] For the example shown in FIG. 8, the values of s and R2 arevaried to produce the correct value of radial offset (s) and slit width(2×R2) so that the inner edge of blade 35 is moved in steps from closeto the center of the ablation (starting at approximately 0.6 mm from thecenter) to the edge of the corrected optical zone at approximately 2.5mm. R, (the iris radius) is fixed at a predetermined value (3 m in onespecific procedure), and s and R2 are chosen to anchor the edge of theablation at the outer edge of the intended transition zone ofapproximately 5 mm radius. The number of pulses for each successiveposition of the inner edge is calculated to give the desired depth fromthe hyperopic lens equation. For a procedure requiring the least numberof pulses, the treatment is ended as soon as the inner edge of theaperture reaches the boundary of the corrected optical zone. Initially,the slit width is set to a maximum value and the imaging lens 51 ispositioned laterally of the axis of rotation 52 such that the inner slitedge is positioned at the minimum distance from the center of theoptical zone and the intersections of the iris diaphragm 32 and theouter slit edge are positioned over the outer edge of the intendedtransition zone.

[0073] The image of the aperture is now ready to be scanned over theanterior surface of the cornea. While several different scanningsequences are possible, the following sequence has been actuallyimplemented with effective results. The radial position along theoptical zone is broken into a series of discrete, equidistant (typically0.1 mm apart) nodes. The number of pulses required to ablate tissue tocut depth C(r) at a node adjacent to the edge of the inner slit iscalculated using

n=(π*δC(r _(n))/θ_(i)(r _(n))*d)

[0074] where n is the number of pulses, δC(r_(n)) is the differencebetween the actual ablation depth from previous pulses and the desiredablation depth at the node, θ_(i) (r_(n)) is the half angle coverage ofthe aperture at r_(n) as previously defined. The radial ablation profilefrom previous pulses is calculated by summing the ablation depth fromprevious positions and pulses at each node as described by equation I.For the initial position, δC(r_(n))=C(r). The number of pulses requiredfor each subsequent node is calculated for each node adjacent to theinner cylinder blade as the blade moves toward the edge of the opticalzone. Having determined the correct number of pulses at each node, thetreatment must be smoothed rotationally to ensure that it is correct andfree from aberrations.

[0075]FIG. 9 is a schematic view of the delivery system optics in anembodiment. As seen in this Fig., the beam from laser 28 is reflected bya first mirror 71 and a second mirror 72, and enters a spatialintegrator 73, where the beam is modified in cross-section. Adiffractive optic may be used to modify a cross section of the laserbeam as described in co-pending application entitled Laser DeliverySystem and Method with Diffractive Optic Beam Integration, U.S. patentapplication Ser. No. 09/015,841 filed on Jan. 29, 1998, the fulldisclosure of which is incorporated herein by reference. The modifiedbeam exiting from spatial integrator 73 is reflected by mirrors 74 and75 and passed through a dove prism 76 to the iris/slit mechanism 78which contains the variable width slit and variable diameter irisdescribed above. The profiled beam exiting from the unit 78 is reflectedby a mirror 79 and enters the image offset control unit 80 whichcontains imaging lens 51. The offset profiled image exiting from unit 80is reflected from a mirror 82 onto the patient's eye. To smooth outfluctuations in beam energy across the beam area, dove prism 76 isrotatably mounted, and is typically rotated during beam generationeither continuously or between pulses.

[0076] The invention affords great flexibility in performing varioustypes of corrections by virtue of the fact that the system can beprogrammed to accommodate patients having differently sized physical eyeparameters and refractive and presbyopic correction requirements. Thevariable slit width/variable diameter iris arrangement is particularlyadaptable for use in the simultaneous treatment of presbyopia,hyperopia, hyperopic astigmatism and irregular refractive aberrations.For simultaneous treatment of presbyopia, hyperopia and hyperopicastigmatism, the ablation geometry is solved as a function of radialdisplacement and angular position of the aperture image about therotational center. Further, in all procedures requiring a smoothing ofthe transition zone at the periphery of the ablation zone, the diameterof the iris is varied over a predetermined range along with the slitwidth variation. For presbyopia and refractive aberrations, a devicesuch as a spatially resolved refractometer or a topography machine orboth may be used to map the irregular surface contour of the cornea todetermine the exact surface corrections required. Thereafter, the slitwidth and the iris diameter can be programmed such that cornealsculpting will achieve the desired aspheric surface geometry on a healedcornea. Alternatively, a wavefront sensor may be used to map theirregular refractive aberrations of the eye. One suitable embodiment ofsuch a wavefront sensor is the Hartmann-Shack sensor described in U.S.Pat. No. 5,777,719, the entire disclosure of which is hereinincorporated by reference.

[0077] For any of the above specific correction procedures, a treatmenttable is normally constructed. The treatment table contains the value ofall of the discrete radial and angular positions of the optomechanicalelements used to scan the image over the relevant portion of theanterior corneal surface. This table also contains the number of laserpulses per position. A typical treatment table contains on the order ofabout 500 different entries.

[0078] The treatment table for a given procedure may incorporate specialfeatures designed to improve the efficiency of the procedure. Forexample, for some procedures (e.g., simultaneous hyperopic andpresbyopic correction) it can be beneficial to leave a small zonecentered on the optical zone untreated. This can be done by constrainingmotion of the inner cylinder blade to guarantee occlusion in the smallzone of interest. The diameter of the untreated zone varies from about0.1 to 1.5 mm, is preferably from about 0.5 to 1.0 mm and is ideallyabout 0.7 to 0.9 mm. Also, standard tables can be constructed for aspecific procedure—e.g., hyperopic correction—to different Dioptriccorrection values, and these standard tables can be sorted and combinedto perform multiple repetitions of one or more standard tables to effecta given Dioptric correction. For example, standard tables may be createdfor a myopic correction for values of ¼, ½ and 1 Diopter. Using thesetables, a 3.75 Diopter correction would proceed by performing thestandard 1 Diopter correction three times, followed by the ½ Dioptercorrection and the ¼ Diopter correction.

[0079] While the invention has been described above with specificreference to ablation of an anterior corneal surface, various portionsof the cornea may also be treated using the invention. For example, theepithelium may be mechanically removed by scraping, as is typically donein photorefractive keratectomy, and the exposed surface may be ablated.Further, the invention can also be used for laser keratomileusis ofcorneal lamella removed from the cornea. This procedure is described inU.S. Pat. No. 4,903,695, issued Feb. 27, 1990, entitled “Method andApparatus for Performing a Keratomileusis or the Like Operation.”

[0080] In applying the invention to this procedure, a flap of cornealtissue is physically removed (either fully or partially) from thecornea, the size of the removed portion typically lying in the rangefrom about 8 to 10 mm wide and a variable thickness up to 400 microns.This flap of tissue is typically removed using a microkeratome. Next,the flap is placed in a suitable fixture—typically an element having aconcave surface—with the anterior surface face down. Thereafter, therequired ablation is performed on the reverse exposed surface of theflap, after which the ablated flap is repositioned on the cornea.Alternatively, after the flap is removed from the cornea, the exposedstromal tissue of the eye can be ablated according to the invention,after which the flap is reattached over the freshly ablated stromaltissue.

[0081] The technique of shaping a cornea is further illustrated in FIGS.10-15. These figures illustrate measured ablation profiles, intendedoptical corrections and measured anterior corneal surface opticalcorrections. The effect of the spatial variance of ablation on ablationshape is illustrated in FIG. 10. A measured ablation shape is plotted asa function of radial position over the ablated optical zone. This figureillustrates an ablated optical zone using an ablation algorithm thatassumes a uniform layer of tissue is removed with each laser beam pulse.The intended optical correction is a +3 D optical correction 410.However, illustrated ablated optical zone 420 is significantlydifferent. The ablated optical zone 420 is overcorrected by about 100%in the central ablation zone 422. The ablated optical zone 420 is overcorrected in the peripheral ablation zone 424 by about 60%. The initialshape of ablated optical zone 420 differs significantly from the healedanterior surface shape, and the healed shape substantially corrects theinitial hyperopic refractive error of the eye.

[0082] The covering and healing of the ablated surface decrease thedifference between the intended optical correction and the anteriorcorneal surface optical correction as illustrated in FIG. 11. A measuredanterior corneal surface optical correction is plotted as a function ofradial position over an ablated optical zone. The anterior opticalcorrection 430 of the healed cornea more closely matches the intended +3D spherical optical correction 410. However, errors between the intendedoptical correction 410 and the anterior surface optical correction 430are still present. The central anterior optical correction 432 is overcorrected compared to the intended +3 D spherical optical correction410. This over correction of the central optical correction 432 is byabout 25% relative to the intended +3 D optical correction, andcorresponds to a 0.75 D near-vision correction at 2 mm. However, theperipheral anterior optical correction 434 is slightly under correctedrelative to the intended +3 D optical correction. This correction of theperipheral anterior optical correction 434 appropriately providesdistance vision correction. Therefore, the anterior optical correction430 is multifocal and will provide some correction of presbyopia. Thismultifocal effect occurs because the ablated shape compensates forchanges in corneal shape as the cornea heals. The peripheral ablatedoptical zone is overcorrected to provide distance vision on a healedcornea. The central optical zone is overcorrected to provide near-visionon the healed cornea. Commercially available corneal topography systemsmeasure healed anterior corneal surfaces. Examples of such systemsinclude the Atlas Corneal Topography System™ available from HUMPHREYINSTRUMENTS of San Leandro, Calif. and the PAR CTS System™ availablefrom PAR VISION SYSTEMS CORPORATION of New Hartford, N.Y.

[0083] The effect of the covering and corneal healing of an ablatedoptical zone is illustrated in FIG. 12. This figure illustrates thedifference in shape between an ablated shape and the final anterioroptical correction on the anterior surface of the cornea. Thisdifference in shape is described as a healing-induced change 440 shownin FIG. 12. The healing-induced change 440 is illustrated for a patienttreated for +3 D of hyperopia. The ablated shape is partially filled inby covering and healing to form the anterior optical correction.However, this partial filling is not constant over the ablated opticalzone. The center of the ablated optical zone shows less filling than theperipheral optical zone. The peripheral optical zone is filled in byabout 50% while the central optical zone is filled in by about 30%. Aperipheral filling 444 is greater than a central filling 442. Proximityto the ablated transition zone causes the peripheral optical surface tobe a different shape than the underlying ablated peripheral opticalzone. However, the anterior central optical surface is distant from theablated transition zone. Therefore, the shape of the anterior centraloptical surface more closely matches the shape of the ablated centraloptical zone. With the above differential healing, an optical zoneablated to a substantially spherical shape for correcting hyperopia willheal to an aspheric shape that corrects for presbyopia.

[0084] By estimating a healing-induced change, an initial ablatedsurface shape may be derived from a desired anterior corneal surfaceshape and a healing-induced change as illustrated in FIG. 13. Forexample, consider a desired anterior surface correction 450 thatcorrects for +3 D of hyperopia and corrects for presbyopia with acentral zone providing +3 D of near-vision correction. The desiredanterior surface correction 450 is also illustrated in FIG. 13. Aninitial ablated surface shape 460 is calculated from the healing-inducedchange 440 and the desired anterior surface correction 450. The initialablated shape 460 for the desired anterior surface correction 450 isillustrated in FIG. 13. The initial ablated shape 460 is overcorrectedrelative to the desired anterior surface correction. The initial ablatedshape 460 is calculated by multiplying the desired anterior surfacecorrection 450 by the ratio of the ablated shape 420 to the healed shape430. A processor may be used to generate the ablated shape in responseto the desired correction input by the system operator, typically makinguse of the embedded computer of the laser workstation, the PCworkstation, and/or the programming and hardware of an externalcomputer.

[0085] The ablated shape may be restricted or reduce relative to adesired anterior surface correction to obtain the desired anteriorsurface correction. The diameter of the relative restriction is betweenabout 0.1 and 2 mm, preferably between about 0.2 and 1 mm and is ideallybetween about 0.3 and 0.7 mm. In an exemplary embodiment thisrestriction is about 0.5 mm as illustrated in FIG. 14. After covering anablated corneal surface feature (such as a presbyopia correction) andallowing healing of a cornea, an anterior surface correction may extendbeyond the initial ablated dimensions of the ablated surface feature.Ablated central zone 470 on reference 480 includes dimension 472 acrossthe central ablated zone. Ablated central zone 470 also includeselevation 474 relative to the reference 480. Reference 480 may be anysuitable reference such as a spherical reference surface on an anterioroptical surface or an ablated surface. Covering of ablated central zone470 and healing of the cornea will form a central anterior opticalsurface 490. Central anterior optical surface 490 includes dimension 492across the central anterior optical surface and elevation 494 relativeto reference 480. A 1.5 mm dimension 472 across the ablated central zone470 will typically extend to a 2 mm dimension 492 across the centralanterior optical surface 490. Therefore, to form a 2 mm central anterioroptical surface, the ablated central zone is preferably restricted by arelative amount of about 0.5 mm. Also, it may be desirable to increasethe elevation 474 of the ablated feature by a relative amount asillustrated above. For example, an ablation intended to produce a 4 umsurface elevation 494 relative to a reference 480 on the anteriorsurface of a healed cornea may be over ablated as an 8 um surfaceelevation 474 relative to a reference 480. This overcorrecting of theablated feature is by a relative amount of 4 um. Relativeover-correction ranges from about 1 to 25 um. A desired final 2 mmdiameter zone on an anterior surface to correct for near-vision with 3 Dmight typically have an elevation of about 4 um. To correct presbyopiausing such a healed shape (in other words, to produce a central zonehaving a diameter of about 2 mm and an elevation of about 4 um on theanterior surface of a healed cornea), a central ablation zone having arestricted diameter of about 1.5 mm and an overcorrected elevation ofabout 8 um is ablated onto an exposed surface of the cornea. Althoughthe term “diameter” is used to indicate a lateral dimension of thesefeatures (and in general in this application), it should be understoodthat the features need not necessarily be circular.

[0086] In some instances, it may be desirable to treat presbyopia byleaving a central region of the optical zone untreated as illustrated inFIG. 15. A small untreated zone 500 centered on the optical zone 502 ofan ablated cornea has a dimension 504 across the untreated zone. Theuntreated zone 504 is smoothed by covering and healing of the cornea andcontributes to the formation of a central anterior optical surface thatcorrects presbyopia.

[0087] The above techniques can be used to calculate initial ablationshapes for treating conditions besides hyperopia and presbyopia. Thesetechniques may be used to calculate the initial ablation shapes used totreat astigmatism, myopia and irregular refractive aberrations of theeye. For example, the higher order aberration terms of an irregularrefractive aberration may be over corrected on an ablated comeal surfaceto form an anterior surface on a healed cornea with a desired opticalcorrection of the higher order aberrations.

[0088] The above technique of making a multifocal optical correction onthe anterior surface of the cornea can be applied to both eyes of apatient to provide an improved correction of presbyopia with binocularvision. The correction of presbyopia preferably covers about a 3 Drange. However, with binocular vision this approximately 3 D range ofpresbyopia correction may be treated by treating each eye with amultifocal optical correction having less than the full 3 D range ofpresbyopia correction. In this case, the average refraction of each ofthe two eyes is different to provide clear vision over the full 3 Drange. A first eye is corrected for near-vision, and a second eye iscorrected for distance vision. The multifocal anterior optical surfaceprovides improved focus for objects intermediate to near and far-vision.For example, one eye is treated to have an average refraction of−0.75 Dwith a 1.5 D multifocal range of focus. This eye has an effective focusfrom 0 to −1.5 D. The other eye is treated to have an average refractionof about −2.25 D with a 1.5 D multifocal range of focus. This eye has aneffective focus from about −1.5 D to −3 D. The effective range of focusof the two eyes combined is about 3 D. The multifocal range on each eyevaries between about 0.5 and 2.0 D, and is preferably between about 1.0and 1.5 D. The difference between the average refraction of the two eyesvaries between about 0.5 and 2.5 D, and is preferably between about 1and 2 D.

[0089] While the above provides a full and complete disclosure of thepreferred embodiments of the invention, various modifications, alternateconstructions and equivalents may be employed as desired. For example,while the invention has been described with specific reference to thesystem of FIGS. 4 through 9, other systems may be employed, as desired.Further, lasers of other appropriate wavelengths than laser 28 may beused, if desired and effective. Also, laser systems which operate on theprinciple of thermal ablations, such as lasers having wavelengths lyingin the infrared portion of the electromagnetic spectrum, may be used toimplement the invention. In addition, while the radial and angularpositioning of the profiled beam is accomplished with imaging lens 51 inthe preferred embodiment, other optical scanning elements—such asrotating mirrors and prisms—may be employed, if desired. Therefore, theabove description and illustrations should not be construed as limitingthe invention, which is defined by the appended claims.

What is claimed is:
 1. A method of treating a cornea of an eye of apatient to mitigate presbyopia, the eye having a pupil and a cornea, themethod comprising: identifying a multifocal ablation shape having afirst region providing a near vision correction and a second regionproviding a far vision correction; adjusting an ablation cut profile ofthe multi focal ablation shape in response to the size of the pupil soas to provide a balance of the near vision correction provided by thefirst region and the far vision correction provided by the second regionfor the patient; ablating the eye with a series of laser beam pulsesaccording to the adjusted ablation cut profile.
 2. The method of claim1, wherein the ablation cut profile further comprises a third regionproviding an intermnediate optical surface having an optical powercontinuously varying between the first region providing near visioncorrection and the second region providing far vision correction, so asto provide intermediate vision correction with the intermediate opticalsurface.
 3. The method of claim 2, wherein the intermediate opticalsurface varies from a first optical power near the first region to asecond optical power near the second region.
 4. The method of claim 3,wherein the difference in optical power between the first optical powernear the first region and the second optical power near the secondregion has a range from about 1 to 4 D.
 5. The method of claim 1,wherein the first region is disposed centrally in relation to the pupilof the eye.
 6. The method of claim 1, further comprising scaling theablation cut profile in relation to the size of the pupil.
 7. The methodof claim 6, wherein the step of scaling of the ablation cut profile isdone so as to scale the optical power of the ablation cut profile inrelation to the size of the pupil.
 8. The method of claim 7 wherein theoptical power of the first region remains constant during the step ofscaling.
 9. The method of claim 7 wherein the optical power of thesecond region remains constant during the step of scaling.
 10. A systemfor treating a cornea of an eye of a patient to mitigate presbyopia witha multifocal ablation shape, the eye having a pupil and a cornea, thesystem comprising: a laser for making a beam of an ablative lightenergy; a processor in electrical communication with the laser andcontrolling a distribution of a series of laser beam pulses to ablatethe multifocal shape on the eye, the multifocal ablation shape producinga first region of the cornea providing a near vision correction and asecond region of the cornea providing a far vision correction, theprocessor determining the distribution of laser beam pulses in responseto a signal related to a size of the pupil so as to balance the nearvision correction and the far vision correction of the multifocaltreatment for the patient.
 11. The system of claim 10 wherein the firstregion providing near vision correction is disposed centrally inrelation to the pupil of the eye.
 12. The system of claim 10 wherein thenear vision correction and the far vision correction are balanced with avariable of a refractive correction in response to the size of thepupil.
 13. The system of claim 11 wherein the variable of the refractivecorrection includes a dimension across the refractive correction. 14.The system of claim 10 wherein the near vision correction and the farvision correction are balanced in response to the size of the pupil soas to scale a dimension across the first region providing near visioncorrection in relation to the size of the pupil.
 15. The system of claim10 wherein the near vision correction and the far vision correction arebalanced in response to the size of the pupil so as to scale a dimensionacross the second region providing far vision correction in relation tothe size of the pupil.